1. Field of the Invention
The present invention relates to a magneto-resistance effect element for writing and reading an information signal on magnetic storage media, a magneto-resistance effect head comprising the magneto-resistance effect element, a magneto-resistance transducer system comprising the magneto-resistance effect head, and a magnetic storage system comprising the magneto-resistance transducer system. More particularly, the present invention relates to a magneto-resistance effect element that reduces noise in a read signal.
2. Description of the Related Art
Conventionally disclosed is a magnetic read transducer that is referred to as a magneto-resistance sensor (hereinafter referred to as an MR sensor) or a head. This magnetic read transducer can read data from a magnetic surface at high linear densities. The MR sensor allows the read element to vary the electrical resistance as the function of the strength and the orientation of a magnetic flux applied from the outside in order to measure a variation in electrical resistance, thereby detecting a magnetic signal.
Such a conventional MR sensor operates based on the anisotropic magneto-resistance effect (hereinafter referred to as an AMR effect). By this effect, the component of a change in electrical resistance of the read element varies in proportion to the second power of the cosine of the angle between the orientation of magnetization and the direction of the sense current flowing through the read element. The AMR effect is described in more detail in an article entitled “Memory, Storage, and Related Applications”, D. A. Thompson, IEEE Transactions on Magnetics, Vol. MAG-11, No. 4, pp. 1039 (1975).
In addition, disclosed lately is a more prominent magneto-resistance effect by which a change in electrical resistance of the layered magnetic sensor is caused by spin-dependent transportation of conduction electrons between magnetic layers via a non-magnetic layer and spin-dependent scattering associated therewith at layer boundaries. This magneto-resistance effect is identified by various names such as the “giant magneto-resistance effect” or the “spin valve effect”. Such a magneto-resistance sensor is formed of suitable materials to provide improved detection sensitivity and greater changes in electrical resistance in comparison with a sensor which makes use of the AMR effect. In a MR sensor of this type, in-plane resistance between a pair of ferromagnetic layers separated by a non-magnetic layer varies in proportion to the cosine of the angle between the orientations of magnetization of the aforementioned pair of ferromagnetic layers. In Japanese Patent Laid-Open Publication No. Hei 2-61572 submitted in July 1988, for claiming priority, described is a layered magnetic structure for providing a significant change in MR caused by an anti-parallel alignment of the orientations of magnetization in the magnetic layers.
On the other hand, such a phenomenon has been recently discovered in which a relative change in orientation of magnetization of ferromagnetic bodies disposed above and below a very thin insulation layer (barrier layer) through which a tunneling current flows, causes a change in electrical resistance. And, the layered structure made up of the ferromagnetic layer, the barrier layer, and the ferromagnetic layer is termed a ferromagnetic tunnel junction. For example, ferromagnetic tunnel junctions are introduced in “Journal of Applied Physics”, Vol. 79 (8), No. 15, pp. 4724 (1996).
On the other hand, in a shield type element that makes use of a ferromagnetic tunnel junction, it is necessary to conduct a sense current for detecting a change in electrical resistance of the element in perpendicular relation to the tunnel junction. However, the structure similar to the shield type element employing the conventional spin valve presents a problem that the sense current flows through a vertical bias layer for controlling the magnetic domain of the free layer disposed near the tunnel junction to reduce the current flowing through the tunnel junction, thereby providing a reduced change in electrical resistance.
In order to overcome this problem, a read head was disclosed in Japanese Patent Laid-Open Publication No. Hei 10-162327 submitted on Nov. 27, 1996, for claiming priority. The read head, employing a ferromagnetic tunnel junction film, has a structure in which the vertical bias layer is not in contact with the free layer.
FIG. 1 is a fragmentary sectional view illustrating the prior-art ferromagnetic tunnel head described in Japanese Patent Laid-Open Publication No. Hei 10-162327. FIG. 1 illustrates the structure of a patterned ferromagnetic tunnel junction element, or a magneto-resistance effect element 30, having an insulation layer 11 disposed between a vertical bias layer 2b and a free layer 3b. This structure can prevent a sense current from flowing through the vertical bias layer 2b. 
However, since the insulation layer 11 disposed between the vertical bias layer 2b and the free layer 3b acts also as a magnetic separation layer, it is difficult in the magneto-resistance effect element 30 to apply a vertical bias magnetic field of a sufficient magnitude to the free layer 3b. This presents such a problem that the magnetic domain of the free layer 3b is controlled insufficiently to cause the hysteresis of the R-H loop to increase for the shield type sensor, thereby providing a high-noise-level read signal upon reading magnetic information on a storage medium.
In order to overcome this problem, a read head was disclosed in Japanese Patent Laid-Open Publication No. Hei 10-255231 submitted on Mar. 7, 1997, 1996, for claiming priority. The read head, employing a ferromagnetic tunnel junction film, has a structure in which the vertical bias layer is in contact with the free layer.
FIGS. 2 and 3 are fragmentary sectional views of the ferromagnetic tunnel head described in Japanese Patent Laid-Open Publication No. Hei 10-255231. FIGS. 2 and 3 illustrate the structure of a layered body comprising the free layer 3b, the non-magnetic layer 4, and the fixed layer 5, in which the vertical bias layer 2b is in direct contact with the end portion of either the free layer 3b or the fixed layer 5.
However, the structure shown in FIGS. 2 and 3 prevents the following problem. As will be described in the preferred embodiments of the present invention, the read head, which was actually fabricated to the structure shown in FIGS. 2 and 3, caused the sense current to flow into the vertical bias layer 2b and thus insufficiently flow through the non-magnetic layer 4. It is thereby made impossible to provide sufficient output of the sense current. The low output made it impossible to provide sufficient (S/N) ratios and bit error rates. As described above, this structure may make it possible in principle to prevent the sense current from flowing through the vertical bias layer 2b and thereby bypassing the non-magnetic layer 4. However, the vertical bias layer 2b is disposed in close proximity to the end portion of the non-magnetic layer 4 in the layered body made up of the free layer 3b, the non-magnetic layer 4, and the fixed layer 5. Thus, it is difficult to fabricate this structure precisely enough to prevent the sense current from flowing through the vertical bias layer 2b and thereby bypassing the non-magnetic layer 4.